1. Field of the Invention
The present invention relates to a control system for controlling a transmission of a vehicle on the basis of road data of a route to be followed.
2. Related Art
In recent years, there is mounted on an ordinary vehicle a navigation system. This navigation system is constructed such that a map is held as electronic data in a memory medium such as CD-ROM whereas the position of the vehicle is located by the GPS (Global Positioning System) using an artificial satellite or the self-contained navigation (or dead reckoning method). These data are combined to output the present position or moving locus of the vehicle or a route to be followed, visually in a display unit such as the CRT, and to guide the running direction in voices.
The electronic map to be used in the navigation system can be stored not only the data such as the layout of roads, the public facilities or the rivers but also the slopes of roads or the legal regulations on road traffics and further a variety of road data such as the coefficients of friction of road surfaces, as achieved by the actual runs. As a result, the data to be obtained by the navigation system can be used not only to guide the vehicle to a destination but also to control the engine, the transmission, the brake system and the body suspension system while the vehicle is running.
One example is disclosed in JP-B-6-58141. The system, as disclosed, is constructed to change the shift pattern of the automatic transmission on the basis of the road data of a route to be followed, as achieved by the navigation system. For example: the shift is inhibited when a curve is detected ahead of the vehicle; the overdrive stage is inhibited when a mountainous region is detected; and a predetermined downshift is inhibited when the so-called "low-.mu. road" having a low coefficient of road surface friction is detected.
In JP-A-5-322591, on the other hand, there is disclosed a system which is constructed to change a shift pattern of an automatic transmission in accordance with a road slope, as detected by the navigation system. Specifically, the control system for an automatic transmission, as disclosed in the Laid-Open, comprises: running state detecting means for detecting the running state of a vehicle; a navigation system for detecting the data of a road ahead of the vehicle, the running azimuth of the vehicle and the present position of the vehicle; and control means for changing the shift pattern (or the shift diagram) of the automatic transmission into such one for a slope as is adapted for the slope of the road.
According to the system thus disclosed, therefore, when the vehicle is to run toward a road different from the ordinary flat road such as an upslope, a downslope, a curve road or a low-.mu. road, the gear stage, as suited for the road, is set in advance. As a result, the frequency of manual shifts by the driver can be lowered, and the delay in the control can be avoided to improve the drivability.
In the prior art, however, the system is constructed, as described above, such that the vehicle is controlled according to the individual road data on the route to be followed, as detected by the navigation system. As a result, if the road data requiring the so-called "special control" for changing the shift pattern for the upslope/downslope or the curved road are frequently detected, the hunting may occur to repeat the shift, and still the worse the drivability may be deteriorated. In the prior art, on the other hand, the shift pattern may be changed according to the actual running state, or the running control characteristics may be set to predetermined ones by the manual operations. However, the prior art has taken no consideration into the control of the case in which that control interferes with the control based on the data obtained by the navigation system. As a result, the power performance of the vehicle may become different from the intention of the driver to cause a discomfort.